Inductrack configuration

ABSTRACT

A simple permanent-magnet-excited maglev geometry provides levitation forces and is stable against vertical displacements from equilibrium but is unstable against horizontal displacements. An Inductrack system is then used in conjunction with this system to effect stabilization against horizontal displacements and to provide centering forces to overcome centrifugal forces when the vehicle is traversing curved sections of a track or when any other transient horizontal force is present. In some proposed embodiments, the Inductrack track elements are also employed as the stator of a linear induction-motor drive and braking system.

This is a Divisional of U.S. patent application Ser. No. 09/896,579,titled “Improved Inductrack Configuration,” filed Jun. 29, 2001 now U.S.Pat. No. 6,629,503 and incorporated herein by reference.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Departnent ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to magnetic levitation systemsfor moving objects, and more specifically, to an improved magneticlevitation train system.

2. Description of Related Art

Halbach arrays, invented by Klaus Halbach in the 1980s for use inparticle accelerators, represent a maximally efficient way to arrangepermanent-magnet material when it is desired to produce a strongperiodic magnetic field adjacent to the array. The beauty of the conceptis that the effect of the cross-magnetized magnet bars in the array isto enhance the periodic magnetic field at the front face of the array,while canceling it back face of the array. Not only is the fieldenhanced, but analysis shows that in a long array the horizontal andvertical components are nearly purely sinusoidal in their spatialvariation, with negligible higher spatial harmonics. If the Halbacharray is then fabricated from high-field permanent-magnet material, suchas NdFeB, peak fields near the front face of the array of order 1.0Tesla are possible.

Particularly for lower-speed applications of magnetic levitation, suchas for urban train systems, it is desirable to employ systems that aresimple in construction and operation and that have low drag at urbanspeeds. Conventional maglev systems, that is, ones employingsuperconducting coils, or ones requiring servo-controlled electromagnetsfor levitation, appear to fall short on one or more of these counts.

Since it was first proposed the magnetic levitation of trains has beenperceived to offer many potential advantages over conventional traintechnology. Besides the ability of maglev trains to operate a higherspeeds than are deemed possible with wheel-and-rail trains, maglevtrains should require less maintenance and be much smoother-riding andquieter than conventional rail systems. These perceived advantages havestimulated major development programs, particularly in Germany andJapan, to solve the technical and economic challenges of this newtechnology. These decades-long efforts have resulted in impressivedemonstration systems, but as yet have not led to commercially operatingrail systems in these countries. Factors that have slowed the deploymentof high-speed maglev trains based on these technologies includetechnical complexity and high capital cost.

In an attempt to address these issues by taking advantage of newconcepts and new materials, a different approach, called the Inductrack,was proposed. The first-proposed Inductrack disclosed in U.S. Pat. No.5,722,326, titled “Magnetic Levitation System For Moving Objects”,referred to herein as Inductrack I, employs special arrays of permanentmagnets (“Halbach arrays”), on the moving train car to produce thelevitating magnetic fields. These fields interact with a close-packedladder-like array of shorted circuits in the “track” to levitate thetrain car. In this first form of the Inductrack, single arrays movingabove the track produced the levitation. Whereas the Japanese maglevsystem employs superconducting coils and the German system requiresservo-controlled electromagnets for levitation, the Inductrack is basedon the use of high-field permanent magnet material, arranged in aspecial configuration called a Halbach array.

In the Inductrack maglev system Halbach arrays are used, located belowthe train car. When in motion the magnetic field of these arrays theninduces currents in a special “track” made up of close-packed shortedcircuits. Analysis has shown that the combination of the three elements,Halbach arrays, NdFeB magnet material, and close-packed circuits in thetrack result in the possibility of achieving levitation forces in excessof 40 metric tons per square meter of levitating magnets, correspondingto magnet weights of only a few percent of the levitated weight The useof Halbach arrays, high-field magnet material and close-packed circuitsas employed in the Inductrack thus overcomes previous concerns, e.g.,madequate levitation forces, that led to questioning the practicality ofusing permanent magnets for maglev trains.

The theoretical analysis of the Inductrack leads to the evaluation ofsuch quantities as the Lift-to-Drag ratio and the levitation powerrequirements as a function of train speed and of the magnet and trackparameters. For the first-proposed, single-Halbach-array, form of theInductrack, the L/D ratio is given by a simple relationship, given inEquation 1 below.

$\begin{matrix}{\frac{Lift}{Drag} = {{kv}\left\lbrack \frac{L}{R} \right\rbrack}} & (1)\end{matrix}$Here k=2π/λ, where λ(m.) is the wavelength of the Halbach array. Notethat the Lift/Drag ratio increases linearly with the train velocity andthat its slope is determined by the inductance (self plus mutual) andthe resistance of the track circuits. For a ladder-like track, that isone composed of transverse bars terminated at both ends with shortingbuses, typical values for L and R give Lift/Drag ratios of the order of300 at speeds of 500 km/hr typical of high-speed maglev trains. Thisratio is high enough to make the levitation losses small (less than 10percent) of the aerodynamic losses at such speeds. Also, for theInductrack the “transition speed,” the speed at which the lift has risento half its final value (and also the speed where the lift and dragforces are equal) is low, of order a few meters/second (walking speeds).Thus the first-proposed form of the Inductrack would seem well suitedfor high-speed maglev train applications.

However, an examination of the first-proposed form of the Inductrack forits possible use in an urban setting, where the typical speeds are oforder one-tenth of that of a high-speed maglev system, shows that theolder system leaves something to be desired. Now, unless inductiveloading of the track circuits is employed, the Lift/Drag ratio will havedropped to 30 or less. For an urban train car weighing, say, 20,000kilograms, a Lift/Drag ratio of 30 at 50 km/hr corresponds to a dragforce of about 6500 Newtons at a drag power in excess of 90 kilowatts.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simplepermanent-magnet-excited maglev geometry that provides levitation forcesand is stable against vertical displacements from equilibrium but isunstable against horizontal displacements.

It is another object to provide an Inductrack system used in conjunctionwith the permanent-magnet-excited maglev geometry to effectstabilization against horizontal displacements and to provide centeringforces to overcome centrifugal forces when the vehicle is traversingcurved sections of a track or when any other transient horizontal forceis present.

Another object of the present invention is to employ Inductrack trackelements as the stator of a linear induction-motor drive and brakingsystem.

Still another object of the present invention is to provide an alternatedesign of a linear pole system that has improved levitating forcecapabilities and lessened lateral stabilizer force requirements.

Another object of the invention is to provide a track for use with alinear pole array, where the track has improved properties for shieldingthe moving levitator poles from the effects of weather and from debristhat might be deposited on the track.

Another object of the invention is to provide the levitating action byusing a Halbach array attached to the moving object where the array isattracted upward to an iron-plate guideway and to further providestabilizing means using additional Halbach arrays comprised of an upperHalbach array and a lower Halbach array, with an Inductrack tracklocated between them.

These and other objects will be apparent to those skilled in the artbased on the disclosure herein.

One embodiment of the present invention is a simplepermanent-magnet-excited maglev geometry that provides levitation forcesand is stable against vertical displacements from equilibrium but isunstable against horizontal displacements. An Inductrack system is thenused in conjunction with this system to effect stabilization againsthorizontal displacements and to provide centering forces to overcomecentrifugal forces when the vehicle is traversing curved sections of thetrack or when any other transient horizontal force is present. In someproposed embodiments, the Inductrack track elements are also employed asthe stator of a linear induction-motor drive and braking system.

This new configuration eliminates the need for centering wheels, exceptpossibly when the car is at rest in the station or upon failure of thedrive while in transit. In such cases, below a low critical speed, thewheels would restrain the system from lateral motion beyond a limit setby a predetermined spacing of the wheels from their guide rails.

One embodiment of the new configuration includes linear pole assemblieswith iron poles, excited by permanent-magnet material. These elementsare mounted on the moving car. They interact magnetically with the polefaces of a linear track, also fabricated from magnetic material, such asiron or steel. As shown, the poles exert a levitation force when theyare displaced downward from the matching (attracting) poles on thetrack. The sideways attractive force exerted by each pole is balanced,when in the centered position, by the attractive force from the matingpole. This system is unstable against transverse displacements from thecentered position. In this embodiment, lateral stabilization is providedby Inductrack Halbach arrays and the associated track circuits. As longas the car is moving so that the various elements are in the centeredstate, no currents will be induced in the Inductrack track, so thatlosses will be minimal. Only when there is a deviation from the centeredposition will currents be induced. Thus the energy losses from thesystem should be substantially less than those of a conventionalInductrack system, where currents must flow to provide the necessarylevitation forces. In addition, the car will always be magneticallylevitated, whether at rest or in motion, something that is not the casein the conventional Inductrack system.

Damping of vertical oscillations is provided by covering the face of thetrack magnet poles with a thin aluminum sheet. The planar Inductrackcircuits may also function as the stator of a linear induction motorsystem using powered electromagnets on the moving car.

An alternate design of the linear pole system is provided that hasimproved levitating force capabilities and lessened lateral stabilizerforce requirements. The track portion of this linear pole array hasimproved properties for shielding the moving levitator poles from theeffects of weather and from debris that might be deposited on the track.

In an alternate embodiment of the invention, the levitating action isprovided by a Halbach array attached to the moving object The array isattracted upward to an iron-plate guideway. Stabilizing means areprovided by additional Halbach arrays comprised of an upper Halbacharray and a lower Halbach array, with an Inductrack track locatedbetween them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a modified Inductrack configuration of the presentinvention.

FIG. 2 shows an alternate Inductrack configuration of the presentinvention.

FIG. 3 shows a rail structure for an Inductrack system of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an improved Inductrack configuration andrepresents a combination of the Inductrack principle of operation withanother magnetic levitation configuration. The new combinationrepresents an improvement in certain properties that is not achievableby either of the two configurations taken alone. The general Inductrackprinciple employed in some embodiments of this new idea is covered inU.S. Pat. No. 5,722,326, “Magnetic Levitation System for MovingObjects,” R. F. Post, incorporated herein by reference.

Other embodiments of the present invention employ the Inductrack IImagnet configuration described in a U.S. patent application Ser. No.09/896,583, filed Jun. 29, 2001, now U.S. Pat. No. 6,664,880, titled,“Improved Inductrack Magnet Configuration” incorporated herein byreference. The magnet configuration of the above incorporated patentapplication is referred to sometimes herein as “Inductrack II”, whereindual arrays are used, one on each side of track circuits.

The general concept involved in this new idea is as follows: A simplepermanent-magnet-excited maglev geometry that is stable against verticaldisplacements from equilibrium but is unstable against horizontaldisplacements is employed to provide levitation forces. An Inductrack IIsystem is then used in conjunction with this system to effectstabilization against horizontal displacements and to provide centeringforces to overcome centrifugal forces when the vehicle is traversingcurved sections of the track or when any other transient horizontalforce is present. In some proposed embodiments the Inductrack trackelements are also employed as the stator of a linear induction-motordrive and braking system.

Horizontal stabilization has required the use of a system of wheels thatrun on the track and thereby supply the necessary centering forces. Theuse of such wheels limits the speed of the maglev system and introducesissues of frictional losses, and mechanical failure from wear withassociated maintenance costs.

This new configuration eliminates the need for centering wheels, exceptpossibly when the car is at rest in the station or upon failure of thedrive while in transit. In such cases, below a low critical speed, thewheels would restrain the system from lateral motion beyond a limit setby a predetermined spacing of the wheels from their guide rails.

One embodiment of the new configuration is shown schematically inFIG. 1. This embodiment includes linear pole assemblies 10 with ironpoles, excited by permanent-magnet material 12. These elements aremounted on the moving car 14. They interact magnetically with the polefaces of a linear track 16, also fabricated from magnetic material, suchas iron or steel. As shown the poles exert a levitation force when theyare displaced downward from the mating (attracting) poles on the track.At the same time, the sideways attractive force exerted by each pole isbalanced, when in the centered position, by the attractive force fromthe mating pole. However, as dictated by Earnshaw's theorem, this systemis unstable against transverse displacements from the centered position.In this embodiment, lateral stabilization is provided by the InductrackII Halbach arrays 18 and the associated track circuits 20. In thefigure, a pair of Halbach arrays (mounted on the car) are shown, with astationary vertical Inductrack II element located between them in theconfiguration as described in the copending patent application. As longas the car is moving so that the various elements are in the centeredstate, no currents will be induced in the track 20, so that losses willbe minimal. Only when there is a deviation from the centered positionwill currents be induced. Thus the energy losses from the system shouldbe substantially less than those of a conventional Inductrack system,where currents must flow to provide the necessary levitation forces. Inaddition, the car will always be magnetically levitated, whether at restor in motion, something that is not the case in the conventionalInductrack system.

Damping of vertical oscillations could be provided by covering the faceof the track 16 magnet poles with, e.g., a thin aluminum sheet. Othermaterials may be used as well, e.g., copper or thicker stainless steel.Eddy currents induced in this sheet by vertical displacements wouldprovide the damping forces.

As noted above, the planar Inductrack circuits shown could also do dualservice as the stator of a linear induction motor system using poweredelectromagnets on the moving car.

Thus, an embodiment of the present invention consists of a combinationof a permanent-magnet-excited linear pole levitation system and avertically oriented Inductrack II system, used here as a lateralstabilizer for the levitation system. An alternate improved design ofthe linear pole system is now provided, one with both improvedlevitating force capabilities and lessened lateral stabilizer forcerequirements. In addition, the stationary “track” portion of this linearpole array has improved properties for shielding the moving levitatorpoles from the effects of weather and from debris that might bedeposited on the track. It also offers a simple means of switching fromone track system to another with minimal displacement of the trackelements.

The improved linear-pole levitation magnetic geometry is shownschematically in FIG. 2. The “rail,” to be fabricated of magneticallysoft iron or steel, is “C-shaped,” with its open gap on the lower side.Within this structure the levitating element, cantilevered from themoving car, is shown as an assembly (not to scale), consisting ofpermanent-magnet material 32 laminated with thin magnetically softmaterial 34. This magnetic configuration has the property of minimizingthe leakage flux from the magnet pole so as to maximize the liftingforce on that pole caused by the proximity of the stationary poleelements.

In this new structure, the levitating force exerted on the moving poleis increased due to the reduction in leakage flux that the new polestructure affords.

As can be seen, the new “rail” is configured so as to protect the movingpole assembly from snow and ice and from debris that might be depositedon the rail. Another desirable property of this levitating configurationis that the levitating force is, to lowest order, independent of lateraldisplacement of the levitated pole, since the decrease in levitatingforce of, say, the left-side pole, caused by lateral motion (from acentered position) to the right, is compensated by a correspondingincrease in the levitating force from the right-side pole. Also, in thecentered position the lateral forces from the left-side and right-sidepoles balance out, and the spatial derivative of the force is reduced.

Finally, the proposed “rail” pole structure should lend itself toswitching of the moving car to another track through the simpleexpedient of moving down the end of an appropriately long section of therail (supported fixedly at its other end) by a few inches, so as to matewith a lower rail that would lead to a siding or to another line. Theassociated Inductrack stabilizer “track” would need only to be madesufficiently high in the switched section of track to accommodate tothis extra vertical motion.

FIG. 3 shows an alternate embodiment of the present invention. Thelevitating action is provided by Halbach array 40 attached to the movingobject 42. Array 40 is attracted upward to an iron-plate guideway 44.Here the levitating Halbach arrays are oriented 90 degrees to the usualorientation used in the Inductrack, i.e., the direction of theirperiodicity is transverse to the direction of motion. In thisorientation the magnetic field will be constant (except at the sides andends of the Halbach array bars) in the direction of motion of the car,thus reducing the parasitic eddy currents induced in the iron guideway.Note that the congruence of the edges of the Halbach array and the ironguideway will provide strong centering forces for transversedisplacements. Orienting the Halbach arrays 90 degrees to the usualorientation has the advantage of reducing eddy currents but the Halbacharrays could operate equally effectively in other orientations such asin the same direction as the Inductrack Halbach arrays.

Since the levitating configuration is unstable against verticaldisplacements (as dictated by Earnshaw's theorem), stabilizing means areprovided by the additional Halbach arrays, shown in the figure. Theseare of the form described in the incorporated copending patentapplication, comprised of an upper Halbach array 46 and a lower Halbacharray 48, with a “flat-track” Inductrack track 50 located between them.However, by design, the main levitating force is provided by the formerset of Halbach arrays, so that the second set is called only to providestabilization, i.e., to provide an up or down force as needed to keepthe system at the desired levitation separation.

It would be a simple matter to incorporate an adjustment means on thelevitating Halbach arrays so that they are “trimmed” to nearly the rightforce level to levitate a given load. This addition would further reducethe stabilizing force needed.

Note also that the Halbach stabilizer shown in FIG. 3 could be replacedby the combined stabilizer/drive-coil configuration described in theincorporated copending patent application. In this way the functions oflevitation, stabilization, and powered-guideway drive could be combinedin one compact assembly. As discussed above, the levitating action isprovided by Halbach array 40 attached to the moving object 42. Array 40is attracted upward to an iron-plate guideway 44.

The propulsion mechanism used in the present invention may be a linearinduction motor. Such a motor generally comprises a coil structure orwinding assembly carried by the vehicle and juxtaposed with a rail offerromagnetic material mounted upon and fastened to the track so that amagnetic path is closed through this rail and, with appropriateenergization of the winding assembly, develops a magnetic forcecomponent in the direction of vehicle propulsion.

The linear motors are, in effect, a linearly-unrolled version of therotary motors. Among currently-known examples of the linear motors are alinear d.c. motor (monopolar or multipolar), linear synchronous motor,linear induction motor and linear pulse motor. Thrust of the linearmotors, corresponding to torque of the rotary motors, generally dependson the structure of the motors. Other propulsion mechanisms are usablein the present invention and will be apparent to those skilled in theart based on the disclosure herein.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best use the invention in variousembodiments and with various modifications suited to the particular usecontemplated. The scope of the invention is to be defined by thefollowing claims.

1. A magnetic levitation system, comprising: a vehicle body; apermanent-magnet-excited geometry operatively attached to said vehiclebody for providing levitation forces upon said vehicle body, whereinsaid geometry is stable against displacements from equilibrium in afirst plane but is unstable against displacements in a second plane; andan inductive track system for providing stabilization againstdisplacements in said second plane, wherein said inductive track systemcomprises: a first Halbach array having a first magnetic field and asecond Halbach array having a second magnetic field, wherein said firstHalbach array and said second Halbach array are magnetically connectedtogether and structurally connected to said vehicle body to form a firstpair of Halbach arrays, wherein said first Halbach array comprisesmagnet configurations positioned with respect to said second Halbacharray and said second Halbach array comprises magnet configurationspositioned with respect to said first Halbach array such that a firstmagnetic flux component of said first magnetic field and a firstmagnetic flux component of said second magnetic field substantiallycancel at a first plane between said first Halbach array and said secondHalbach array, and a second magnetic flux component of said firstmagnetic field and a second magnetic flux component of said secondmagnetic field substantially add at said first plane; a track ofwindings fixedly attached to a stationary support, wherein said track ofwindings is located between said first pair of Halbach arrays; and apropulsion mechanism for moving said first pair of Halbach arrays alongsaid track, wherein when said first pair of Halbach arrays move alongsaid track and said first plane is not located at said track, a currentis induced in said windings and a restoring force is exerted on saidfirst pair of Halbach arrays, wherein said permanent-magnet-excitedgeometry comprises a stationary rail comprising magnetically softmaterial and having an open gap on its lower side, saidpermanent-magnet-excited geometry further comprising a levitatingelement attached to said vehicle, wherein said levitating elementcomprises permanent-magnet material laminated with magnetically softmaterial, wherein said rail and said levitating element exert attractingmagnetic force upon each other.
 2. The magnetic levitation system ofclaim 1, wherein said stationary rail is C-shaped.
 3. A magneticlevitation system, comprising: a vehicle body; apermanent-magnet-excited geometry operatively attached to said vehiclebody for providing levitation forces upon said vehicle body, whereinsaid geometry is stable against displacements from equilibrium in afirst plane but is unstable against displacements in a second plane; andan inductive track system for providing stabilization againstdisplacements in said second plane, wherein said inductive track systemcomprises: a first Halbach array having a first magnetic field and asecond Halbach array having a second magnetic field, wherein said firstHalbach array and said second Halbach array are magnetically connectedtogether and structurally connected to said vehicle body to form a firstpair of Halbach arrays, wherein said first Halbach array comprisesmagnet configurations positioned with respect to said second Halbacharray and said second Halbach array comprises magnet configurationspositioned with respect to said first Halbach array such that a firstmagnetic flux component of said first magnetic field and a firstmagnetic flux component of said second magnetic field substantiallycancel at a first plane between said first Halbach array and said secondHalbach array, and a second magnetic flux component of said firstmagnetic field and a second magnetic flux component of said secondmagnetic field substantially add at said first plane; a track ofwindings fixedly attached to a stationary support, wherein said track ofwindings is located between said first pair of Halbach arrays; and apropulsion mechanism for moving said first pair of Halbach arrays alongsaid track, wherein when said first pair of Halbach arrays move alongsaid track and said first plane is not located at said track, a currentis induced in said windings and a restoring force is exerted on saidfirst pair of Halbach arrays, wherein said permanent-magnet-excitedgeometry comprises a Halbach array connected to said vehicle, saidgeometry further comprising a stationary iron plate guideway above saidHalbach array to which said Halbach array is attracted.
 4. The magneticlevitation system of claim 3, wherein said first plane is asubstantially horizontal plane, wherein said second plane is asubstantially vertical plane, wherein the edges of said Halbach arrayand said iron guideway are congruent to provide centering forces fortransverse displacements.
 5. The magnetic levitation system of claim 3,wherein said inductive track system comprises two substantiallyhorizontally disposed Halbach arrays fixedly attached to said vehicle,said Inductrack I system further comprising a stationery track betweensaid two substantially horizontally disposed Halbach arrays.
 6. Themagnetic levitation system of claim 3, wherein said Halbach arraycomprises a size relative to said iron plate guideway that is adjustedto provide a desired levitating force.
 7. The magnetic levitation systemof claim 5, wherein said track of windings and said two horizontallydisposed Halbach arrays are configured to operate as a linear inductionmotor assembly.